Characterization of Genotoxicity of Kojic Acid by Mutagenicity in Salmonella and Micronucleus Induction in Rodent Liver

Abstract

Three lots of kojic acid (KA) which were produced for use as a reagent, food additive and in cosmetics were shown to be mutagenic in S. typhimurium TA100 with or without S9 mix, with a speciˆc activity of around 100 revertants per mg of KA. Since there are contradictory reports on genotoxicity of KA, we examined, using HPLC, whether the mutagenicity to S. typhimurium is due to KA itself, or due to contaminants present in the KA samples. Although two UV absorbing fractions were separated by HPLC, mutagenicity was detected only in the major fraction and the speciˆc mutagenic activity of KA did not change before and after HPLC separation. The material in the major peak fractions on HPLC was conˆrmed to be KA by NMR. Thus it was demonstrated that KA itself is mutagenic and no mutagenic contaminants were detected in the three lots of samples. Since KA is known to produce liver tumors in mice, we further examined the genotoxicity of KA in the liver of rodents. KA induced micronuclei (MN) in the regenerating liver of adult mice by its gastric intubation at 1 g per kg body weight. However, no MN were induced in young mice (3 weeks old) without partial hepatectomy. Since it was recently found that KA had no tumor-initiating activity in the liver of mice in a two-step carcinogenicity study, there is no evidence that the genotoxicity detected in the mouse liver is involved in liver carcinogenesis.

Final Report of the Safety Assessment of Kojic Acid as Used in Cosmetics

“…The mutagenicity of kojic acid was studied in S typhimurium strain TA 100, with and without S9. 77 To rule out the possibility that mutagenicity observed in earlier studies was due to contaminants in kojic acid samples, the researchers purified 3 samples of kojic acid (reagent, food additive, and cosmetic lots) by high-performance liquid chromatography (HPLC) and tested the resulting fractions. In the mutation assay, kojic acid was tested at 500, 1000, and 1500 mg/plate.…”

Evaluation of in vitro Genotoxic Potential of Kojic Acid in Human Lymphoblastoid Cells

“…Nohynek et al (14) demonstrated that kojic acid was mutagenic in S. typhimurium TA 98, TA 100, TA 1535, TA102 and E. coli WP2uvrA, but not in TA 1537 by the standard Ames test. Ishikawa et al (15) demonstrated that three diŠerent lots of samples of kojic acid were mutagenic in S. typhimurium TA100 and their mutagenicities were derived from kojic acid itself, but not from any contaminants. In mammalian cell systems, kojic acid induced chromosome aberrations and sister chromatid exchanges in Chinese hamster ovary CHO cells with and without S9 mix (10).…”

In vivo Genotoxic Potential of Kojic Acid in Rodent Multiple Organs Detected by the Comet Assay

“…Therefore, it would be premature to conclude that its hepatic genotoxicity detected by the comet assay in both species contradicts to negative responses in the two-step carcinogenicity studies with both species. In our previous study, kojic acid induced micronuclei in regenerating liver of partially hepatectomized mice (9). Considering our previous observation that the comet assay-detectable DNA lesions can form chromosome aberrations in human lymphoblastoid WTK1 cells (10), it is interesting that both comet assay-detectable DNA damage and micronuclei were induced in mouse liver, which is a possible target organ of kojic acid carcinogenicity.…”

“…These facts suggest the possibility that kojic acid acts on hepatocytes as an initiator in mice and leads to the induction of hepatocelluar tumors. Although kojic acid induced micronuclei in the liver of regenerating mouse liver (9), no micronuclei were observed in regenerating rat liver and infant rat liver without partial hepatectomy (15).…”

“…Although kojic acid is not used as a food additive now, it is mainly used as a cosmetic agent for skin whitening properties (6,7) because of its inhibitory actions on human melanocyte tyrosinase (8). Kojic acid which is known to be genotoxic without microsomal activation, inducing mutation in bacteria and mammalian cells, chromosome aberrations in mammalian cells, and DNA damages detected by comet assay in mammalian cells (9,10) has been reported to induce hepatic tumors in mice (11), although no long-term carcinogenesis studies in rats have been reported. The initiation activity in the liver has been investigated in two step carcinogenesis studies of rats and mice.…”